Fix python-ext

[hoodmane]

So far this gets the algebra crate compiling successfully. Not sure whether it works or not.

TODO:

• [ ] resolution
• [ ] resolution-homomorphism
• [ ] upgrade Pyo3 to 0.16.1

[dalcde]

I think it would be helpful to get partially wokring code merged, together with some tests to prevent breakage, to avoid merge conflicts piling up.